A couple of things of note here. First in this 1907 drawing Smith called for a bore diameter of .650" which is well under the nominal of .662". in later drawings this size was increased.
2nd the taper of the forcing cone figures to .150" per inch on the diamter. Based on the listed size of end of chamber & bore the 12 would have a cone of .460" length while the 16 would have one of .547", even though the angle is identical for each. SAAMI Specs have for sometime given a max angle here of 5°. This would give a taper to the cone's diameter of .175" per inch. With same specs as for above this would give a cone length in the 12 of .394" and in the 16 of 469".
I just checked the bore diameters on a 16ga Baker Black Beauty & A Lefever 16ga H grade. The Baker measured .663" with the Lefever going a bit oversize @ .670". Both have 28" barrels & both weigh in @ 6 3/4lbs. Neither are super lightweights but both handle & shoot well.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra